A turbine is a turbomachine which converts the internal energy (enthalpy) of a flowing fluid (liquid or gas) into rotational energy and ultimately into mechanical drive energy. A part of the internal energy of the fluid flow is extracted therefrom by the laminar flow, which is as swirl-free as possible, around the turbine blades, said part of the internal energy being transferred to the rotor blades of the turbine. Via the latter, the turbine shaft is then set into rotation, and the useful power is transmitted to a coupled working machine, for example to a generator. The rotor blades and the shaft are part of the movable rotor of the turbine, said rotor being arranged within a housing.
As a rule, a plurality of blades are mounted on the shaft. Rotor blades mounted in a plane each form a blade wheel or rotor wheel. The blades are profiled in a slightly curved manner, similarly to an airplane wing. Upstream of each rotor wheel there is usually a stator wheel. These guide vanes project from the housing into the flowing medium and cause it to swirl. The swirl (kinetic energy) generated in the stator wheel is used in the subsequent rotor wheel in order to set the shaft, on which the rotor wheel blades are mounted, into rotation.
The stator wheel and rotor wheel together are designated a stage. Often, a plurality of such stages are connected in series. Since the stator wheel is stationary, and the guide vanes are fastened to the outside of the housing, a seal with respect to the shaft of the rotor wheel has to be established, in order to keep losses as low as possible.
To this end, the guide vanes are held on the rotor-side by sealing rings in the form of a cylinder casing. Said sealing rings usually consist of a plurality of segments, usually ten. These are pushed onto a hook connector at the head of the guide vanes (tongue-and-groove connection) and in this way seal off the hot-gas duct from the rotor. In order to prevent displacement in the circumferential direction, the sealing ring segments are fixed individually by bolts which each project radially into one of the guide vanes.
On account of given tolerances between blades and sealing rings, said tolerances being necessary for the thermal expansion that is normal in operation, relative movement is possible. In this case, it has been shown that, as a result of dynamic excitations, considerable wear can arise on the sealing ring segments. The findings extend here from simple wear, which makes replacement during scheduled maintenance necessary, to massive wear, which can result in forced maintenance involving replacement of the sealing ring or can also result in turbine damage involving blade damage.
It is known practice here to provide the sealing ring segment with elastic elements that act on the guide vanes by means of a restoring force. Extensive disk springs are arranged for this purpose in U.S. Pat. No. 7,645,117, and leaf springs, which have a curvature or wave shape in the azimuthal or axial direction, such that the corresponding pretension arises, are used in US 2008/0019836, US 2011/0135479 and EP 1 441 108.
However, a disadvantage with the known sealing ring segments is that, when leaf or large disk springs are used, extensive pretension is always applied to a plurality of guide vanes. This makes it difficult to mount the guide vanes. In addition, the strength of the restoring force is not individually settable or re-adjustable.